Doors and windows on a building sustain the influences from the environment which are mainly wind pressure and invasion of rain and snow, and also sustain the opening and closing force while in use as well as self gravity. The wind force is the main reason that enables the rod pieces (cross bar, vertical stile and window lattice serving as lattice profiles), frames and sashes to bend and deform. Safety of the doors and windows are mainly decided by the ability of the doors and windows for sustaining the wind force, and is usually measured according to the gas pressure value sustained in unit area.
The mechanical properties of rigid PVC plastic which is namely a PVC profile is far poorer than that of steel, aluminum and wood. Particularly, the bending strength of the PCV profile is only ¼ of that of the wood product, 1/28 of that of the aluminum product and 1/84 of that of the steel product; under the same section shape and size, the bending property of the PVC profiled bar is much poorer than that of the aluminum profiled bar and the steel profiled bar. In order to makeup this defect, one important measure is to additionally arrange steel enhancement profiled bar which is namely a steel lining in the empty cavity of the PVC profile.
Additionally arranging the steel lining can solve the problem of insufficient intensity of the PVC profile, but also brings some negative defects.
Usually, the steel linings and the PVC profiles are separately stored. When installing the doors and windows, the installation personnel needs to fix the steel linings and the PVC profiles in the job site, thus increasing the assembling procedure of installing the doors and windows. Moreover, the site installation personnel need to have corresponding technologies and proficiency. Consumption of a number of steel products causes severe wastes inevitably. Moreover, there are certain requirements for storage and transportation of the steel products, for example, attention needs to be paid to water prevention, keeping cleanness of the steel products, and keeping far away from articles having corrosion effect, and the like. More importantly, because the steel lining is metal which is a good conductor of heat, the heat transfer coefficient of the PVC doors and windows is increased, and the thermal insulation performance of the PVC doors and windows is reduced, which is not beneficial for thermal insulation and energy conservation.